Our previous research has shown that a specific human breast gross cystic disease fluid protein of 15,000 dalton monomer molecular size (GCDFP-15) is also present in a proportion (40%) of human breast carcinomas and the protein is uniformally present in all normal apocrine glands. It is our hypothesis that breast carcinomas which produce GCDFP-15 are derived from breast epithelium capable of undergoing apocrine metaplasia and the expression of GCDFP-15 by the carcinoma cells is a biochemical index of an aprocrine epithelial function. Thus the breast carcinomas which produce GCDFP-15 are a subclass of breast carcinomas and they may have specific pathological and clinical attributes which, when understood, may help refine diagnosis and treatment for this disease. This proposal is for an immunoperoxidase staining study of GCDFP-15 in breast carcinomas. Our findings will be correlated with a number of clinical and pathological features of the breast carcinomas. The pathological features for correlation are: pathological subtype of carcinoma; growth pattern; and hormonal receptor status. Biological behavioral characteristics of the carcinomas for correlation are: disease free interval; sites of metastatic recurrence; and response to various forms of hormonal and chemical therapy for metastatic disease. Genetic-environmental factors for correlation are: patient age, race, menopausal status, family history of breast carcinoma and personal history of benign or prior malignant breast disease. This study will be conducted as a retrospective analysis of breast carcinoma tissue specimens which are already in our pathology files as permanent paraffin blocks. Patients whose breast carcinomas are to be analyzed for GCDFP-15 content by immunoperoxidase staining will have been in follow-up with serial blood level measurements of this tumor marker. Clinical parameters for correlation with the immunoperoxidase staining will be obtained by chart review.